Southern Maryland in the context of "Maryland Route 4"

Charles County is a county located in the U.S. state of Maryland. As of the 2020 United States census, the population was 166,617. The county seat is La Plata. The county was named for Charles Calvert (1637–1715), third Baron Baltimore. The county is part of the Southern Maryland region of the state. With a median household income of $103,678, Charles County is the 39th-wealthiest county in the United States as of 2020, and the highest-income county in the United States with a Black-majority population.

St. Mary's County, established in 1637, is a county located in the U.S. state of Maryland. As of the 2020 census, the population was 113,777. Its county seat is Leonardtown. The name is in honor of Mary, the mother of Jesus. St. Mary's County is part of the Lexington Park, MD Metropolitan Statistical Area, which also is included in the Washington-Baltimore-Arlington, DC-MD-VA-WV-PA Combined Statistical Area. It is part of the Southern Maryland region.

The county was the home to the first Maryland Colony, and the first capital of the Colony of Maryland. Settled by English Catholics, it is considered to be the birthplace of religious freedom in North America, at a time when the British colonies were settled primarily by Protestants. The county is home to the Patuxent River Naval Air Station and St. Mary's College of Maryland. Traditionally, St. Mary's County has been known for its unique and historic culture of Chesapeake Bay tidewater farming, fishing, and crabbing communities. But with the advent of the military bases, growth of an extensive defense contractor presence, and the growth of St. Mary's College of Maryland, as well as increasing numbers of long-distance Washington, D.C. commuters, it has been undergoing a decades-long transformation which has seen the county's population double since 1970.

Prince George's County (often shortened to PG County, PG, or PGC) is located in the U.S. state of Maryland bordering the eastern portion of Washington, D.C. As of the 2020 U.S. census, the population was 967,201, making it the second-most populous county in Maryland, behind neighboring Montgomery County. The 2020 census counted an increase of nearly 104,000 in the previous ten years. Its county seat is Upper Marlboro. It is the most populous African American-majority county in the United States, as well as the second most affluent behind neighboring Charles County.

The county is part of the Capital region of the state, though portions of the county are considered to be in Southern Maryland. The county also hosts many federal governmental facilities, such as Joint Base Andrews and the United States Census Bureau headquarters.

U.S. Route 301 (US 301) in the state of Maryland is a major highway that runs 122.85 miles (197.71 km) from the Governor Harry W. Nice Memorial Bridge over the Potomac River into Virginia northeast to Delaware. It passes through three of Maryland's four main regions: Southern Maryland, the Baltimore-Washington Metropolitan Area, and the Eastern Shore. US 301 serves mainly as a bypass of Baltimore and Washington, D.C. from Virginia to Delaware.

U.S. Route 301 (US 301) is a part of the U.S. Highway System that runs from Sarasota, Florida, to Biddles Corner, Delaware. In Virginia, the U.S. Highway runs 142.70 miles (229.65 km) from the North Carolina state line near Skippers north to the Maryland state line at the Potomac River near Dahlgren. US 301 forms the local complement to Interstate 95 (I-95) from Emporia to Petersburg. The U.S. Highway runs concurrently with US 1 between Petersburg and the state capital of Richmond, where the highways form one of the main north–south avenues. US 301 continues north concurrent with Virginia State Route 2 (SR 2) to Bowling Green, forming an eastern alternative to I-95 and US 1 north of Richmond. At Bowling Green, which is connected to I-95 by SR 207, US 301 becomes the primary highway connecting Richmond and the Northern Neck with Southern Maryland. US 301 was constructed in four main segments: as the original SR 24 and then US 17-1 south of Petersburg, as US 1 from Petersburg to Richmond, as SR 2 from Richmond to Bowling Green, and as part of SR 207 toward Dahlgren. US 301 replaced US 17–1 in the early 1930s and was extended from Petersburg north along its current course into Maryland when the Potomac River Bridge was completed in 1940.